Two separate approaches will be utilized to characterize the changes in the micro-circulation associated with the development of diabetes in man. The distribution of small blood vessels will be examined in the bulbar conjunctiva of the eye by taking serial 35mm photographs with a special medical Nikor lens and reconstructing a complete mosaic of the entire vascular bed from enlargements (40X). Morphometric analysis procedures are then used to determine capillary density (L/A), capillary spacing (diffusion distance), degree of coiling or tortuisity of venules, etc. In addition, micorvessel flow will be determined from video tape recordings using a two window raster line procedure and electronic cross-correlation of the signals. Clear cut differences have been found in the distribution of microvessels of diabetes in that the microvessels below 20 microns in diameter increase in density with time, whereas in age matched non-diabetics controls, the capillary density remains in a fairly constant range from 20 to 60 years of age. BIBLIOGRAPHIC REFERENCES: Zweifach,B.W. and H.H. Lipowsky. Microvascular resistances based on direct measurements of pressure and flow. In: "Cardiovascular System Dynamics". (J.Boon, A. Nordergraaf and J. Raines, ed.), M.I.T. Press, 1977. Hargens, A.R. and Zweifach, B.W.: Contractile stimuli in collecting lymph vessels. (In press, Amer. J. Physiol., 1977).